Tensioner with spring force control in a second bore

Abstract

A tensioner for tensioning a chain span which uses two pistons. The movement of the two pistons may be coupled together. The first piston provides damping to the chain span and a second piston provides variable, dominant and automatically adjusting spring force to the chain span. The tensioner automatically adjusts the mean tension force to keep the chain tension as low as possible without sacrificing chain control, significantly improving drive efficiency at new chain conditions and conditions with dynamic loads.

What is claimed is: 
     
       1. A tensioner for a passive tensioner system tensioning a span of chain or a belt, comprising:
 a housing having a first axially extending bore with a first fluid input, and a second axially extending bore with a second fluid input; 
 a first piston slidably received by the first axially extending bore, the first piston comprising a body having a first end and a second end; 
 a first pressure chamber for biasing the first piston outwards from the housing, defined between the first piston and the first axially extending bore and in fluid communication with the first fluid input; 
 a hollow moveable sleeve slidably received by the second axially extending bore, comprising a hollow body having a first open end and a second open end separated by an inner flange having a top surface and a bottom surface; 
 a second piston having a body coaxially arranged within the moveable sleeve and received by the first open end of the movable sleeve; 
 a second piston spring for biasing the second piston outwards from the moveable sleeve, received by the first open end of the moveable sleeve, having a first end contacting the second piston and a second end contacting the top surface of a flange of the moveable sleeve; 
 a bias spring for biasing the moveable sleeve outwards from the housing, received within the second open end of the moveable sleeve with a first end of the bias spring in contact with the bottom surface of the inner flange of the moveable sleeve and a second end in contact with the second axially extending bore of the housing; 
 a second pressure chamber defined between the bottom surface of the inner flange of the moveable sleeve and the second bore, in fluid communication with the second fluid input; and 
 a check valve between the second pressure chamber and the second fluid input; 
 wherein when dynamic load from the chain or belt moves the first piston and the second piston inwards and outwards from the housing, fluid from the second fluid input is drawn into the second pressure chamber through the check valve, creating a fluid pressure in the second pressure chamber, causing the movable sleeve to move outwards from the housing and exert an outward force on the second piston through the second piston spring, opposing an inward force of the dynamic load. 
 
     
     
       2. The tensioner of  claim 1 , wherein the first piston and the second piston are coupled for movement together. 
     
     
       3. The tensioner of  claim 2 , wherein the first piston and the second piston are coupled for movement together by coupling the body of the first piston and the body of the second piston. 
     
     
       4. The tensioner of  claim 2 , wherein the first piston further comprises an extension having a top surface and a bottom surface, wherein the second piston pushes on the bottom surface of the extension, coupling the second piston to the first piston for movement together. 
     
     
       5. The tensioner of  claim 1 , wherein the body of the first piston further comprises an open end at the second end of the body and a closed end at the first end of the body, a bottom surface at the open end, and a hollow interior having an inner diameter. 
     
     
       6. The tensioner of  claim 5 , further comprising a first piston spring for biasing the first piston outwards from the housing, received within the hollow interior of the first piston, the first piston spring having a first end contacting the hollow interior of the first piston and a second end contacting the first axially extending bore. 
     
     
       7. The tensioner of  claim 6 , wherein the second piston spring has a greater spring constant than the first piston spring and the bias spring. 
     
     
       8. The tensioner of  claim 5 , further comprising a first volume reducer received by the hollow interior of the first piston and a second volume reduced received within the second open end of the moveable sleeve. 
     
     
       9. The tensioner of  claim 1 , further comprising a first piston spring for biasing the first piston outwards from the housing, the first piston spring having a first end contacting the second end of the first piston and a second end contacting the first axially extending bore. 
     
     
       10. The tensioner of  claim 1 , wherein the first fluid input and the second fluid input are connected to the same fluid supply. 
     
     
       11. The tensioner of  claim 1 , wherein the first fluid input and the second fluid input are connected to different fluid supplies. 
     
     
       12. The tensioner of  claim 1 , further comprising a check valve between the first fluid input and the first pressure chamber. 
     
     
       13. The tensioner of  claim 1 , further comprising a vent for venting fluid from the first pressure chamber. 
     
     
       14. The tensioner of  claim 1 , further comprising a vent for venting fluid from the second pressure chamber. 
     
     
       15. The tensioner of  claim 1 , further comprising at least one pressure relief valve in the first pressure chamber.